Coherent structures in sheared velocity flow

In the magnetized torus Blaamann, coherent structures are known to exist, and their features are reported in previous papers [Øynes et al, Phys. Rev. E, 57 (1995) 2242, Fredriksen et al., Plasma Phys. Contr. Fusion, 45 (2003) 721. Monopolar and dipolar structures are rotating in the poloidal cross-section with ExB velocity. Generally, in Blaamann, the plasma is rotating like a rigid body in most of the cross- section. However, in some localized regions a strong velocity shear is present. In this work, we focus on the analysis of the dynamical evolution of the structures in presence of sheared flow regions. Positive and negative density fluctuating vortical structures survive far away from the velocity shear, while they are partially fragmented across the shear. A statistical analysis suggests, according to numerical papers [Krane et al., Phys. Rev. Lett., 80, 4422, 1998], that vortical structures are stretched and fragmented into smaller scale structures in the proximity of sheared velocity regions. We applied conditional analysis to evidence the interaction of vortex structures with the sheared flow. A quantitative statistical analysis gave the possibility to study the distribution of monopolar positive and negative structures and to understand their general contribution to the transport.